A) Field of the Invention
This invention relates to a technique for recording data by setting an optimum recording power even if a difference in recording velocities of a write-once optical disc and a re-writable optical disc is large.
B) Description of the Related Art
In recent years, a velocity for recording data in a constant linear velocity (CLV) recording optical disc (hereinafter called just an optical disc) like a write-once optical disc like a rewritable optical disc such as a CD-R, a DVD-R and the like and such as a CD-RW, a DVD-RW, a DVD-RAM and the like is on the track of high-speeding. The optical disc is regulated to record data by fixed recording density. Therefore, conventionally, the optical disc has recorded data by a constant linear velocity method (CLV) to record data with fixed transmission velocity. However, as technological advance, a recording method with high recording velocity such as a partial constant angular velocity (partial CAV) method, a zone constant linear velocity (zone CLV) method and a zone constant angular velocity (zone CAV) method has been used.
FIGS. 8A to 8D show relation charts between a radius position and a linear velocity in each recording method. In the partial CAV method, as shown in FIG. 8A, a recording velocity is accelerated by keeping a fixed rotation velocity of the disk (constant angular velocity: CAV) at an inner track side of the disk to be recorded. Then after attaining to the maximum recording velocity, recording is executed with a fixed linear velocity without interruption/resume of recording. In the zone CLV method, as shown in FIG. 8B, an opening from inner part of the disk to be recorded to an outer track is divided to zones (hereinafter called divide), and recording is executed with fixed velocity in the zones. Then interruption/resume of recording is executed for further writing by applying a buffer under run protection technology in a velocity switching position between zones. Moreover, the buffer under run protection technology is a technique to prevent occurrence of a buffer under run error certainly by pausing writing and waiting recovery of a buffer level in a case that writing data amount of buffering is below a fixed level, and by accurately starting further writing from a point paused recording after recovery. In the zone CAV method, as shown in FIG. 8C, an opening from inner part of the disk to be recorded to an outer track is divided to some zones, and recording is executed with fixed angular velocity in the zones. Then interruption/resume of recording is executed to write further by applying a buffer under run protection technology in a velocity switching position between zones.
Also, as high performance of a spindle motor to rotatively drive the optical disc and technological advance of data recording to the optical disc, as shown in FIG. 8D, a full CAV method (hereinafter called CAV method) to record data in a whole area of the optical disc with the CAV method becomes to be used for high velocity recording.
FIG. 9 is a cross sectional view showing an area structure of the CD-R and the CD-RW (hereinafter also called CD-R/RW) that are examples of the optical discs. As shown in FIG. 9, the CD-R/RW has a diameter of 120 mm and a thickness of 1.2 mm. Also, in the CD-R/RW, a section with a diameter from 46 to 50 mm as a lead in area and a section with a diameter from 50 to 118 mm as a program area and a remaining area are provided. The program area can record data up to a section with a maximum diameter of 116 mm.
There is 2.5 times difference between a length of the most inner track in the program area of the CD-R/RW and a length of the most outer track in the program area. Also, the CD-R/RW is an optical disc to record data by fixed recording density as described before. Therefore, when the optical disc is recorded with the CAV method, there will be 2.5 times difference in data transmission velocity between the most inner track and the most outer track in the program area. Therefore, as recording velocity is high, an amount of change in the velocity is large. For example, in the case that recording velocity at the most inner track in the program area is set to be 4 times speed (×4), recording velocity at the most outer track in the program area will be 10 times speed (×10). On the other hand, in the case that recording velocity at the most inner track in the program area is set to be 16 times speed (×16), recording velocity at the most outer track in the program area will be 40 times speed (×40).
When recording in the optical disc is executed by the CAV method, an optimum recording power to irradiate the optical disc needs to be changed sequentially because the linear velocity changes depending on recording areas. Therefore, in the conventional optical disc recording apparatus, the recording velocity from the inner track side to the outer track side is continuously fastened, and the recording power of the optical disc to which the optical disc is irradiated is increased continuously to record data. For example, when recording is executed by the CAV method, the optimum recording power is changed to record according to a linear function Y=aX+b (Y: recording power, X: recording velocity) as a recording power function.
Also, in the conventional optical disc recording apparatus, this recording power function is defined by a following method. FIGS. 10A to 10C are character charts of the recording power function. When fitting the recording power function, an optimum character at each recording velocity by each type of the optical discs is obtained by experimentation, a slope of the recording power function a is fitted by using the average value and a approximate value by a least-squares method. In a first method, the recording power function is determined in accordance with data obtained by performing an OPC at, for example, the minimum recording velocity as shown in FIG. 10A while the optical disc of a type is identified when the data is to be recorded. Also, in a second method, the recording power function is determined by an interpolating/extrapolating linear approximation in accordance with data obtained by performing OPCs at 2 recording velocities as shown in FIG. 10B while the optical disc of a type is identified when the data is to be recorded. Further, in a third method, the recording power function is determined by an interpolating/extrapolating linear approximation in accordance with data obtained by performing OPCs at a minimum recording velocity and a maximum recording velocity as shown in FIG. 10C.
However, in a case that the first method to define the recording power function is used, an area where the power function characteristic is approximately the same as the originally suitable value is only in and around initial power obtained by the OPCs as shown in FIG. 10A, and other part is a approximate value. Therefore, an optimum value may not be obtained. Also, in a case that recording is executed by the CAV method, as described before, as a rotation velocity of the optical disc is high, as this tendency grows because the difference of the recording velocity (amount of velocity change) between the inner track side and the outer track side is getting large.
Also, in a case that the second method to define the recording power function is used, when the difference of the recording velocity between two to execute the OPC is considerably small, the power function characteristic being approximately the same as the originally suitable value is only in and around initial power obtained by the OPC as same as the first method, and other part is an approximate value. Therefore, an optimum value might not be obtained. Also, as described before, as a rotation velocity of the optical disc is high, amount of velocity change between the inner track side and the outer track side is getting large. Therefore, in a case of an optical disc that has a test recording area only in an inner track side, the difference of the recording velocity between two to execute the OPC cannot be enlarged.
For example, in a case that a recording velocity (a linear velocity amplification) is a normal speed, a rotation velocity at the most outer track in the program area is approximately 200 rpm, and the rotation velocity needs to be approximately 500 rpm in order to make a linear velocity at the most inner track in the program area be same as that at the most outer track. In this case, the optical disc can be rotated enough even inner track side. On the other hand, in a case that the recording velocity (the linear velocity amplification) is 48 times speed, a rotation velocity at the most outer track in the program area is approximately 9600 rpm, and the rotation velocity needs to be approximately 24000 rpm in order to make a linear velocity at the most inner track in the program area be same as that at the most outer track. However, when the optical disc is rotated with a velocity of 24000 rpm, there is every possibility of a self-destruction of the optical disc by a self-excited vibration, and it is extremely dangerous. Also, the optical disc apparatus normally does not equip a spindle motor with such a high-speed rotation. Therefore, the OPC can be executed only at two velocities of an executable recording velocity in the test recording area in inner track side.
Therefore, as same as the problem of the above-described first method, the power function characteristic being approximately the same as the originally suitable value is at a velocity obtained the power by the OPC or in the velocity of it. As the recording velocity is away from the velocity to execute the OPC, an optimum recording power will be far different from the value obtained by the power function obtained by extrapolating linear approximation. Therefore, recording with a high quality is difficult.
Moreover, in a case that the third method to define the recording power function, in the optical disc that has a inner test recording area and a outer test recording area, the OPC is executed with a minimum recording velocity in the inner test recording area, and the OPC is executed with a maximum recording velocity in the outer test recording area as shown in FIG. 10C. Then the recording power function can be obtained by an interpolating linear approximation. However, since the recording power function is obtained by linear interpolation, as a difference of the recording velocity between inner and outer track sides is large, an optimum recording power in an intermediate area at a recording velocity will be different from an interpolated power. Therefore, recording with a high quality is difficult.
In addition to the above, in the first to third methods, the recording power function is different depending on a change of an environmental temperature around the optical disc and a wave length of a laser light beam irradiated to the optical disc.